Mark http/tests/serviceworker/getregistrations.html flaky on Mac
Mark http/tests/serviceworker/getregistrations.html flaky on Mac

Expand http/tests/serviceworker/getregistrations.html flakiness line in
TestExpectations to also include Mac, in addition to previous platform.

BUG=503175
TBR=ksakamoto@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/1206973002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@197766 bbb929c8-8fbe-4397-9dbb-9b2b20218538

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk